run = function(name, attributes) 
    local result, error_message = pcall(prun, name, attributes)
    if result then
        error_message = "OK"
    end
    return result, error_message
end

prun = function(name, attributes)
    local value_of_a = demo.get(attributes, "a") 
    print("plugin: the value of key 'a' is: ", value_of_a);
    demo.remove(attributes, "b"); 
    demo.set(attributes, "c", "x"); 
end

